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\title{COMP516 Essay 1: Pretty Good Privacy}
\author{Richard Whitty}

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\begin{abstract}

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\section{INTRODUCTION}

\section{CRYPTOGRAPHY}

Cryptography is the practice of rendering a message unreadable without access to a  secret piece of information. The secret may range from knowledge of the algorithm used to a password or a long number and the algorithms involved range from trivial to extremely complicated.

Cryptographic algorithms can be broadly placed into two groups; Symmetric ciphers - where the same key is used to encrypt a message as to decrypt it and Asymmetric ciphers – where different keys are required for each operation.

Symmetric ciphers are generally used for storing data securely on a users own system, where only that user needs to know the key. They can create an archive of sensitive data, encrypt it with a password known only to them, and save it somewhere.

Asymmetric ciphers are needed if the encrypted data is to be sent to somebody else. The two keys are known as the public key (for encryption) and the private key (for decryption). If user A needs to send a message to B, A first obtains B's public key, encrypts the data using it then sends it to B. When B receives the encrypted message, B uses the private key to decrypt and view the message.

A widely used assymetric cipher is the RSA (Rivest, Shamir and Adleman) algorithm. Much internet communication is based on it (SSL for example), which potentially makes it the most popular such algorithm.


The importance of cryptography in the modern world is paramount, as many communications are performed over networks controlled by an untrusted third party who would otherwise be able to intercept or modify information in transit. Such networks include the postal service, telephone operators and the global internet.

For individuals and businesses it is often necessary to engage in communication where only the intended recipient may view the message and be able to trust in the authenticity of said message. For example e-commerce and financial data, or sensitive personal or business information.

During 2008, in the UK, 519 260 surveillance requests were issued under the Regulation of Investigatory Powers Act 2001 (RIPA). The act includes provisions for monitoring all internet and telephone communication, as well as bugging of houses or stalking people on CCTV. This increased government surveillance is another feature of modern life driving the adoption of cryptographic systems.

Recently there have been some heavily publicized data thefts or losses where computers, tapes or disks containing personal information on many people have gone missing. In nearly all cases the data was not encrypted and would have been easily accessible by the person finding it.

\section{PRETTY GOOD PRIVACY}
Pretty Good Privacy (PGP) is a user interface to a number of encryption algorithms. The main innovation was to make encryption accessible to individual users without in-depth computer knowledge.
%  It was first released in source code form as a book in 1991 by Phil Zimmerman.

The initial version of PGP used the BassOmatic symmetric algorithm, designed by Zimmerman himself. However this was replaced with IDEA after vulnerabilities were discovered.

In version 3, support for asymmetric encryption was added with DSA. CAST5 became the main symmetric cipher due to licencing issues with the IDEA algorithm. The software was also redesigned so that the back-end was cleanly seperated from the front end, allowing multiple user interfaces to use the encryption core.

% 1.How does the Pretty Good Privacy (PGP) system work, and how does it compare with other cryptosystems? 

% 2.How secure is PGP? 
% 3.What are the applications of PGP? 
% 4.What have been the legal issues surrounding PGP and its inventor? 
When Zimmerman published PGP, the export of encryption technology was illegal under US law and he was investigated. Zimmerman subsequently published a book containing the source code, as books were protected under the free speech laws.
Eventually no charges were brought.

In the United Kingdom, encryption poses a more complex problem for individuals, as under RIPA (part 3, section 49), an individual can be compelled to turn over any encryption keys. Recently there were two individuals convicted of refusing to turn over their keys and are awaiting sentence \cite{osc_rep09}.

\section{CONCLUSIONS}
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